Evaluation of brush seals for oil sealing applications

After proven performance in gas turbine secondary flow and hot gas path sealing applications, brush seals are being considered for oil and oil mist applications in aero-engines and industrial turbines. In oil sealing applications shear heating and oil coking are major concerns. The field experience indicates that shear heating and oil coking issues can be managed if seal is designed properly. When seal stiffness is well controlled, combined with proper fiber material selection and leakage cooling, shear heating and oil coking issues can be managed. Field experience from early gas turbine bearing sump applications suggest reduced oil mist ingestion and compressor blade fouling with no observable coking issues. Brush seal operating clearance determines leakage rate and oil temperature rise. Balancing these two conflicting performance criteria requires the knowledge of bristle hydrodynamic lift. In this work, some background on analytical solution to bristle lifting force and shear heating is presented. Based on short bearing approximation, the analytical solution suggests a strong dependence of seal clearance and hydrodynamic lift force on oil temperature and viscosity. The hydrodynamic lift force relation has been expanded to include oil temperature variability due to rotor speed and lift clearance. Results are also compared with the experimental data obtained from the dynamic oil seal test rig.